What to know about bone cancer in the knee

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Bone cancer is a rare type of cancer that happens when cells in a bone begin to grow out of control.

While people may think of bone as solid and unchanging, it constantly dissolves and forms new bone tissue. Osteoclasts are bone cells that dissolve old tissue, and osteoblasts are cells that replace the old tissue with new bone.

Bone cancer may be primary, which means it originates in the bone, or bone metastasis, which is cancer that originates somewhere else in the body and spreads to the bones. Bone metastasis is more common than primary bone cancer.

People also refer to primary bone cancer as bone sarcomas. Sarcomas are cancers that develop in bone, fat tissue, muscle, blood vessels, and fibrous tissue.

Types of primary bone cancers include:

• Osteosarcoma: This is the most common type of primary bone cancer. If someone has bone cancer of the knee, they likely have osteosarcoma. This type of bone cancer usually starts in osteoblast cells.
• Ewing sarcoma: This is the second most common type of primary bone cancer, which most often affects children, adolescents, and young adults. Ewing sarcoma tumors typically develop in pelvic bones, the spine, ribs, shoulder blades, and the long bones of the legs.
• Chondrosarcoma: This type of bone cancer develops in the cartilage cells and typically affects people over 20. It most often develops in the arms, legs, and pelvic bones.

Learn about bone cancer in children here.

The most common symptoms of bone cancer in the knee are:

• Bone pain: Pain may start intermittently and worsen at night. Over time, the pain can become constant and increase with activity. Some people develop a limp from the pain.
• Swelling: This may only develop after a person already feels pain in the area. In some cases, a person may be able to see and feel a lump or mass in the knee.
• Fractures: Although bone cancer can weaken the bones of the knee, fractures are not typical, except in rare cases called telangiectatic osteosarcomas, which can weaken bones more severely.

Learn about the signs of bone cancer in the leg here.

Experts do not know the cause of bone cancer, although researchers have identified various risk factors that may increase a person’s chance of developing it.

Risk factors include:

• Some previous cancer treatments: People who have had radiation therapy, chemotherapy, or stem cell transplantation are more likely to develop osteosarcoma, especially if they received treatment during childhood.
• Genetic change: A certain change in the RB1 gene may increase the risk of bone cancer.
• Certain conditions: Other conditions may also increase a person’s risk of bone cancer, including:
  • hereditary retinoblastoma, an eye cancer
  • Paget disease
  • Werner syndrome
  • Bloom’s syndrome
  • Rothmund-Thomson syndrome
  • having family members with Li-Fraumeni syndrome

A doctor may obtain a person’s medical history, perform a physical exam, order various imaging tests to diagnose bone cancer, and confirm their diagnosis with a biopsy.

Imaging tests may include:

• X-ray
• CT scan
• Bone scan
• MRI scans
• PET scan

To diagnose bone cancer, a doctor will usually perform a biopsy. Types of biopsy include:

• Needle biopsy: A doctor uses a large needle to remove a cylinder of tissue from the affected bone.
• Surgical biopsy: A doctor makes an incision in the skin to reach the tumor and removes a sample of the bone.

Learn more about tests for bone cancer here.

Doctors decide how to treat bone cancer based on its extent. This includes the stage and grade of cancer, a person’s age, general health, and personal preferences.

Treatment may involve:

Surgery

Doctors typically treat osteosarcomas with surgery. Surgeons will usually remove the tumor and some healthy tissue around the tumor. This is to prevent the cancer from recurring and growing again.

In most cases, surgeons can remove the tumor and spare the affected limb. They may replace the bone with bone from another area of the body, or with a prosthesis.

If the tumor is very large or extends into the blood vessels or nerves, surgeons may recommend amputating the affected limb.

Chemotherapy

Doctors usually treat osteosarcomas with chemotherapy for about 10 weeks before surgery. After surgery, a person may require further chemotherapy for up to a year.

Radiation therapy

Doctors do not often use radiation to treat osteosarcoma. However, when doctors cannot remove all the cancer during surgery, they may use radiation to kill the remaining cancer cells.

Below are answers to some frequently asked questions about bone cancer in the knee.

How common is knee cancer?

Bone cancer is rare. Primary bone cancer accounts for less than 1% of all newly diagnosed cancers. Of the types of primary bone cancer, osteosarcoma is the most common.

It typically affects people between the ages of 10–30. However, around 1 in 10 cases of osteosarcoma occurs in people over 60.

Is knee cancer curable?

Yes, people can survive knee cancer, especially if it has not spread to other areas of the body.

The 5-year survival rate for osteosarcoma is 60%, meaning 6 in 10 people live at least 5 years after diagnosis.

The most common type of primary bone cancer in the knee is osteosarcoma, which may cause bone pain, swelling, and in rare cases, fractures.

Treatment often involves surgery and sometimes chemotherapy and radiation therapy. Surgeons may be able to remove all the cancerous tissue and replace the bone with another piece of bone or a prosthesis.

The treatment and outlook can depend on the extent of the bone cancer, a person’s age, and their overall health. 60% of people live for at least 5 years following diagnosis.